System and method for separation of hydrocarbons and contaminants using redundant membrane separators

ABSTRACT

A redundant membrane separation system and method for separating hydrocarbons and contaminants. The redundant membrane separation system includes a system and method wherein the flow of the produced hydrocarbons and contaminants from a production string can be diverted to one of at least two tubes while the membrane separation system in another of the tubes is serviced.

FIELD OF THE INVENTION

[0001] This invention relates to a system and method for separation of hydrocarbons and contaminants using redundant membrane separators.

BACKGROUND OF THE INVENTION AND BRIEF DESCRIPTION OF THE RELATED ART

[0002] Hydrocarbon gases and liquids are recovered from underground wellbores by drilling a wellbore into a hydrocarbon gas or liquid formation and withdrawing the materials under reservoir pressure or by artificial lifting. The fluids withdrawn from the reservoir consist of a combination of hydrocarbon liquids and gases, water, sediments, and other contaminants. The water fraction is commonly referred to as produced water. This fraction, although small at the early stages of oil extraction from most fields, grows over the years and could constitute the majority (up to about 90%) of the fluid that is withdrawn from the reservoir.

[0003] The current recovery technology involves removing the hydrocarbon and any contaminants including water and sediments which are present from the wellbore, and separating the contaminants from the hydrocarbon above ground. This above ground separation is costly. Disposal of the removed contaminants may also present environmental problems. The contaminants which may be produced include carbon dioxide, nitrogen, water vapor, hydrogen sulfide, helium, other trace gases, water, water soluble organics, normally occurring radioactive material and others.

[0004] It would be highly desirable to maintain some or all of the contaminant materials within the wellbore and/or selectively separate the contaminants in the wellbore or subsea flow lines for reinjection, removal, or other processing.

[0005] Membrane technologies have been developed which separate materials by allowing the selective passage of specific materials through the membrane. One example of a membrane separation system for separating oil and water downhole is described in Price, U.S. Pat. No. 4,296,810. The contaminants which are removed may be reinjected into an underground disposal formation or removed to the surface for disposal or other processing. Over time, the membranes that are used become fouled due to accumulation of contaminants. In addition, the production of a particular well may change over time requiring a change in the configuration of the membrane separation system which is used.

[0006] Accordingly, it would be desirable to provide a system and method for separation of hydrocarbons and contaminants which minimizes the costs associated with the maintenance and replacement of the membrane separators.

SUMMARY OF THE INVENTION

[0007] The present invention provides a solution to the costs associated with the maintenance and replacement of membrane separators by using a system and method of redundant membrane separators. The system includes redundant membrane separators located in at least two tubes which are connected to the production string for delivering produced hydrocarbons from the production string to a hydrocarbon collection tank. The flow of hydrocarbons and contaminants can be diverted to one of the tubes while the membrane separation system in another of the tubes is serviced.

[0008] In accordance with one aspect of the present invention, a redundant membrane separation system for separating hydrocarbons and contaminants includes a production string in at least one wellbore producing a mixture of hydrocarbons and contaminants, at least two tubes connected to the production string for delivering the produced hydrocarbons from the production string to a hydrocarbon collection tank, and a membrane separation system for separating hydrocarbons and contaminants located in each of the tubes, wherein the flow of the produced hydrocarbons and contaminants can be diverted to one of the tubes while the membrane separation system in another of the tubes is serviced.

[0009] In accordance with another aspect of the present invention, a redundant membrane separation method for separating hydrocarbons and contaminants includes positioning a production string in at least one wellbore producing a mixture of hydrocarbons and contaminants, connecting at least two tubes to the production string for delivering the produced hydrocarbons from the production string to a hydrocarbon collection tank, placing a membrane separation system for separating hydrocarbons and contaminant in each of the tubes; and diverting the flow of the produced hydrocarbons and contaminants to one of the tubes while the membrane separation system in another of the tubes is serviced.

[0010] The present invention provides a system and method for separation of hydrocarbons and contaminants utilizing redundant membrane separators wherein the flow of hydrocarbons and contaminants can be diverted to another flow line while the membrane separator system is serviced. The separation system and method provide reduced downtime and improved efficiency over systems with a single membrane separator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention will now be described in greater detail with reference to the preferred embodiments illustrated in the accompanying drawings, in which like elements bear like reference numerals, and wherein:

[0012]FIG. 1 is a schematic side cross sectional view of a downhole apparatus for separating hydrocarbons and contaminants;

[0013]FIG. 2 is a perspective view of a membrane separation cartridge for use in the apparatus of FIG. 1;

[0014]FIG. 3 is a side cross sectional view of a redundant membrane separator system for separating hydrocarbons and contaminants according to the present invention;

[0015]FIG. 4 is a side cross sectional view of another embodiment of a redundant membrane separator system for separating hydrocarbons and contaminants according to the present invention;

[0016]FIG. 5 is a perspective view of a redundant membrane separator system located on the sea floor;

[0017]FIG. 6 is a partially cut away perspective view of a tube of the membrane separator system;

[0018]FIG. 7 is a side cross sectional view of another embodiment of a redundant membrane separator system for separating hydrocarbons and contaminants according to the present invention;

[0019]FIG. 8 is a side cross sectional view of another embodiment of a redundant membrane separator system for separating hydrocarbons and contaminants according to the present invention; and

[0020]FIG. 9 is a schematic diagram of a redundant membrane separation method for separating hydrocarbons and contaminants according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Membrane separation systems are used for separating contaminants from hydrocarbon liquids and gases. The contaminants which are removed may be reinjected into an underground disposal formation or removed to the surface for disposal or other processing. Over time, the membranes that are used downhole or in a sea floor separation system may become fouled due to accumulation of contaminants. In addition, the production of a particular well may change over time requiring a change in the configuration of the membrane separation system which is used. The present invention provides a system and method of redundant membrane separators wherein the flow of hydrocarbons and contaminants can be diverted to another flow line while the membrane separation system is serviced.

[0022] Wells generally include a production tubing string or casing which is lowered into the well. The production tubing string may include valves, packers, and other elements for controlling the production of the well. The production tubing string may also include membranes for separation of hydrocarbons and contaminates. However, in order to remove and replace membranes incorporated in the production string, the production string must be withdrawn from the well. This removal of the production string results in substantial downtime and expense. The present invention is designed to reduce the costs and loss of production by the use of redundant membrane separators which eliminate the need to shut the well down.

[0023]FIG. 1 illustrates a membrane separation system 10 positioned in a wellbore 12 for subsurface separation. The separation system includes an outer perforated shell 14 surrounding one or more inner tubes 16 which contain a preferentially selective material. A pair of packings 20 is provided around the shell 14 and a second pair of packings 22 is provided around the inner tubes 16 to isolate a contaminant collection zone 24.

[0024] In operation, the hydrocarbons and contaminants enter the wellbore below the containment collection zone 24 through production perforations 28. The hydrocarbons and contaminants pass through the inner tubes 16. As the hydrocarbons pass through the inner tubes 16, one or more contaminants permeate out of the inner tubes through the preferentially selective material and enter the containment collection zone 24. The hydrocarbons plus any remaining contaminants which were not removed continue out the tops of the tubes 16. The hydrocarbons with reduced contaminants are passed to the surface or to another separation system. The contaminants which have been collected in the collection zone 24 may be disposed of by directing the contaminants through the perforations 26 to an underground disposal formation. Alternatively, an additional tube may be provided for removal of the contaminants from the collection zone 24 to the surface.

[0025]FIG. 2 illustrates one example of a membrane cartridge or element 30 formed of a preferentially selective material for permeating contaminants. The membrane element 30 is tubular element having a central bore 32 through which the hydrocarbons and contaminants pass in the direction indicated by the arrows A. The contaminants permeate out through the preferentially selective material as indicated by the arrows B, while the hydrocarbons continue out the top of the membrane element as indicated by the arrows C. The membrane elements 30 may be stacked within a perforated tube to form the inner tubes 16 or may be interconnected to form a self-supporting tube 16.

[0026] Each one of the stacked membrane elements 30 may be designed to permeate one or more of the contaminants which are present in the well. For example, one membrane element 30 may be designed for removal of carbon dioxide, a second for removal of hydrogen sulfide, and a third for removal of heavy hydrocarbons.

[0027] Although a hollow fiber or tubular shaped membrane formed of multiple membrane elements is illustrated, other membrane shapes may also be used. Some other membrane shapes include spirally wound, pleated, flat sheet, or polygonal tubes. The use of multiple hollow fiber membrane tubes have been selected for their large fluid contact area. The contact area may be further increased by adding additional tubes or tube contours.

[0028] The membrane elements 30 may be stacked in different arrangements to remove contaminants from the flow of hydrocarbon gas in different orders. For example, the bottom membrane elements 30 may be those that remove water and heavy hydrocarbons which may damage some of the gas removal membrane materials. The top membrane elements 30 may be those that remove carbon dioxide and hydrogen sulfide.

[0029] The different contaminants may be removed into a single contaminant collection zone 24 and disposed of together by removal or reinjection. Alternatively, the different contaminants may be maintained in different zones for removal and/or reinjection separately. The membrane elements 30 may be arranged in series or parallel configurations or in combinations thereof depending on the particular application.

[0030] The membrane units 30 may be removable and replaceable by a retrieval tool using conventional retrieval technology such as wireline or coiled tubing. However, when the membrane separation system is replaced the entire well has to be shut down resulting in a loss of production. When a well is serviced that contains only a single membrane separation system such as described in Price, U.S. Pat. No. 4,296,810 or Peachey, U.S. Pat. No. 5,296,153, the entire well has to be shut down and results in a loss of production. The present invention utilizes redundant membrane separators which will result in no loss of production since the well does not need to be shut down during maintenance and replacement of the membrane separation system.

[0031]FIG. 3 illustrates a redundant membrane separation system 70 for separating hydrocarbons and contaminants in a wellbore. The system includes a production string 74 in at least one wellbore 76 producing a mixture of hydrocarbons and contaminants 78. At least two tubes 80 are connected to the production string 74 for delivering the produced hydrocarbons from the production string to a hydrocarbon collection tank 82. A membrane separation system 84 for separating hydrocarbons and contaminants is located in each of the tubes 80.

[0032] In another embodiment, as shown in FIG. 4, the flow of the hydrocarbons and contaminants is controlled by at least one valve or a plurality of valves 90 within the production string 74. The valves 90 can divert the flow of the hydrocarbons and contaminants to one of the tubes 80 while the membrane separation system 84 in the other tube is serviced. The valves 90 can be located above and/or below the membrane separation system 84 to control the flow of hydrocarbons and contaminants.

[0033] In an alternative embodiment, also shown in FIG. 4, the flow of the hydrocarbons and contaminants can be monitored and controlled by an intelligent automation system 92. The intelligent automation system 92 monitors the temperature, pressure, and concentration of hydrocarbons and contaminants flowing in the wellbore. Accordingly, based on readings obtained from the sensors of the intelligent automation system the intelligent automation system 92 controls the opening and closing of the values 90 which directs the flow of hydrocarbons and contaminants into separate tubes and adjusts the flow rate.

[0034] In another embodiment, the redundant membrane separation system 98 as shown in FIG. 5 has a central gathering station 100. The central gathering station 100 is connected to the production strings in one or more wellbores. In a sub sea situation the one or more production strings are connected to each wellhead 102 and the wellheads are connected to the central gathering station 100. The central gathering station 100 is connected to at least two tubes 104 for delivering the produced hydrocarbons from the production string to a hydrocarbon collection tank 106. In this case, the collection tank 106 is located on board a tanker. However, it shall be appreciated that the collection tank 106 can be located on the seafloor, or any other location which can accommodate a collection tank. A membrane separation system 108 for separating hydrocarbons and contaminants is located in each of the tubes 104. The tubes 104 may be flexible to adjust for the changing sea conditions. As in the embodiments discussed above, the separation system may include valves, and/or intelligent automation system.

[0035]FIG. 6 is a partially cut away perspective view of a portion of one of the tubes 104 of the membrane separation system 108 of FIG. 5.

[0036] In an alternative embodiment, illustrated in FIG. 7, the contaminants are delivered to a disposal formation 110 by a tube 114, or by a disposal string 112 to a collection tank 116 above ground. The disposal of the contaminants can be controlled by valves, an intelligent automation system or a combination thereof.

[0037] As will be recognized by one skilled in the art, the present invention can be used with any retrievable membrane system. For example, the present invention could be used with a retrievable membrane separation system as illustrated in U.S. patent application Ser. No. 09/640,573 filed Aug. 17, 2000. The disclosure of U.S. patent application Ser. No. 09/640,573 is incorporated herein by reference in its entirety.

[0038] In operation, as shown in FIG. 8, the membrane separation system 200 is placed inside the production tubing (not shown) of a well and can be easily deployed by a deployment tool and retrieved by a retrieval tool without the removal of the entire production string. In one embodiment the membrane separation system 200 includes a bottom sub 212, a seal assembly 214, one or more shear-out subs 230, one or more membrane units 220, a packoff assembly 216, and a fishing neck 260. The system may also include outer tubular members including a perforated liner 218, a packoff bushing 219, and a tube 254 for delivery of the hydrocarbon to the surface. The assembled separation system 200 is inserted inside the production tubing of a well and the bottom sub 212 is inserted into a packer 256 in the production tubing. An optional upper packer 258 may be added for isolation of the separated contaminants if the contaminants are to be disposed of downhole.

[0039] In an assembled configuration, each of the membrane units 220 includes one or more membranes (not shown) positioned inside the membrane unit. Each of the membranes separates one or more hydrocarbon and one or more contaminant. The membranes are hollow tube membranes positioned inside each of the membrane units 220. The membrane units 220 are connected to one another and to one or more of the shear-out subs 230 to form the separation string or system 200 which is inserted into the production tubing in the wellbore.

[0040] When the membranes become fouled, an increase in the amount of contaminants produced may be observed indicating that the membranes should be replaced. Other detection methods may also be used to detect fouling of the membranes. In addition to replacement of membranes when they have become fouled, it may be desirable to remove the separation system for alterations, modifications, or updates when the production of the well changes or when improved technologies become available.

[0041] The membrane units 220 may be removable and replaceable by a retrieval tool using conventional retrieval technology such as wireline or coiled tubing. A wireline retrieval tool includes a grasping portion which grasps the fishing neck sub 260 and pulls the separation string out of the production tubing. The fishing neck sub 260 functions as a receptacle for the grasping portion of the wireline retrieval tool. A coiled tubing retrieval system operates in a similar manner.

[0042] The wellbore and the production tubing in the wellbore may include curves and irregularities which can cause the separation string to become stuck during retrieval. If a portion of the separation string becomes stuck in the production tubing during removal, the shear-out sub 230 shears off at a predetermined tension load leaving the fishing neck 250 of the shear-out sub exposed. The retrieval tool is then lowered into the production tubing to retrieve a remainder of the separation string by grasping the fishing neck 250 of the shear-out sub 230. The removed membranes may be cleaned for reuse or discarded.

[0043] In FIG. 9, a redundant membrane separation method for separating hydrocarbons and contaminants 300 is shown. The method includes the steps of positioning a production string in at least one wellbore producing a mixture of hydrocarbons and contaminants 302, and connecting at least two tubes to the production string for delivering the produced hydrocarbons from the production string to a hydrocarbon collection tank 304. A membrane separation system for separating hydrocarbons and contaminant is placed in each of the tubes 306, and the flow of the produced hydrocarbons and contaminants is diverted to one of the tubes while the membrane separation system in another of the tubes is serviced 308.

[0044] In another embodiment, the redundant membrane separation method for separating hydrocarbon and contaminants further includes the step of grasping and removing one of the membranes separation systems with a retrieval tool while the flow of hydrocarbons and contaminants continues to flow through the other membrane system.

[0045] It should be understood that the number, type and configuration of the valves, intelligent completion devices and membrane separation systems may vary depending on the particular wells. The redundant separation system may be specifically designed for a particular well taking into account the type and amounts of hydrocarbons and contaminants present in the well or formation, and the well configuration(s).

[0046] In addition, the description of the present invention and drawings have been illustrated with respect to a vertical well, however, it should be understood that the invention may be employed in horizontal wells and other non-vertical wells.

[0047] While there has been described what are believed to be the preferred embodiment of the present invention, those skilled in the art will recognize that other and further changes and modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the true scope of the invention. 

What is claimed is:
 1. A redundant membrane separation system for separating hydrocarbons and contaminants, the system comprising: a production string in at least one wellbore producing a mixture of hydrocarbons and contaminants; at least two tubes connected to the production string for delivering the produced hydrocarbons from the production string to a hydrocarbon collection tank; and a membrane separation system for separating hydrocarbons and contaminants located in each of the tubes, wherein the flow of the produced hydrocarbons and contaminants can be diverted to one of the tubes while the membrane separation system in another of the tubes is serviced.
 2. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 1, wherein the flow of hydrocarbons and contaminants can be diverted by at least one valve.
 3. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 1, wherein the flow of hydrocarbons and contaminants can be diverted by a plurality of valves.
 4. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 1, wherein the flow of hydrocarbons and contaminants is monitored by an intelligent automation system.
 5. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 4, wherein the intelligent completion device controls the flow of hydrocarbons and contaminants into the tubes.
 6. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 3, wherein the valves are connected to an intelligent automation system for diverting the flow of the hydrocarbons and contaminants.
 7. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 1, wherein the tubes are flexible.
 8. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 1, wherein a central gathering station is located between the production string and the tubes.
 9. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 8, wherein the central gathering station is connected to the production string in a first of the at least one wellbore and to a second production string in a second wellbore.
 10. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 8, wherein the central gathering station is on the sea floor.
 11. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 1, wherein the membrane separation system removes at least one contaminant from the hydrocarbon with a system including a first preferentially selective material positioned within the tube and a second preferentially selective material positioned within the tube, wherein the first preferentially selective material is permeable to a different material than the second preferentially selective material.
 12. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 1, wherein the contaminants are removed from the tubes.
 13. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 1, wherein the contaminants are delivered to a disposal formation.
 14. The redundant membrane separation system for separating hydrocarbons and contaminants according to claim 1, wherein the contaminants are delivered to a disposal string.
 15. A redundant membrane separation method for separating hydrocarbons and contaminants, the method comprising: positioning a production string in at least one wellbore producing a mixture of hydrocarbons and contaminants; connecting at least two tubes to the production string for delivering the produced hydrocarbons from the production string to a hydrocarbon collection tank; placing a membrane separation system for separating hydrocarbons and contaminants in each of the tubes; and diverting the flow of the produced hydrocarbons and contaminants to one of the tubes while the membrane separation system in another of the tubes is serviced.
 16. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, further comprising the step of diverting the flow of hydrocarbons and contaminants by at least one valve.
 17. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, further comprising the step of monitoring the flow of hydrocarbons and contaminants by an intelligent automation system.
 18. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 17, further comprising the step of controlling the flow of hydrocarbons and contaminants into the tubes using the intelligent automation system.
 19. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, wherein the tubes are flexible.
 20. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, wherein a central gathering station is located between the production string and the tubes.
 21. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 20, wherein the central gathering station is connected to the production string in a first of the at least one wellbore and to a second production string in a second wellbore.
 22. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 20, wherein the central gathering station is on the sea floor.
 23. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, wherein the membrane separation system removes at least one contaminant from the hydrocarbon with a system including a first preferentially selective material positioned within the tube and a second preferentially selective material positioned within the tube, wherein the first preferentially selective material is permeable to a different material than the second preferentially selective material.
 24. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, further comprising the step of delivering the contaminants to a disposal formation.
 25. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, further comprising the step of delivering the contaminants to a disposal string.
 26. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, further comprising the step of removing one of the membrane separation systems for servicing.
 27. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, further comprising the step of continuing a flow of hydrocarbons to the hydrocarbon collection tank while one of the membrane separation systems is serviced.
 28. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, further comprising the step of removing and replacing a membrane element of the membrane separation systems.
 29. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, further comprising the step of servicing the membrane separation system and replacing the membrane separation system in one of the tubes.
 30. The redundant membrane separation method for separating hydrocarbons and contaminants according to claim 15, further comprising the step of grasping and removing one of the membrane separation systems with a retrieval tool while the flow of hydrocarbons and contaminants continues to flow through the other membrane separation system. 